Sen. Barack Obama of Illinois was elected the nation's 44th president yesterday, riding a reformist message of change and an inspirational exhortation of hope to become the first African American to ascend to the White House.

Obama, 47, the son of a Kenyan father and a white mother from Kansas, led a tide of Democratic victories across the nation in defeating Republican Sen. John McCain of Arizona, a 26-year veteran of Washington who could not overcome his connections to President Bush's increasingly unpopular administration.

Standing before a crowd of more than 125,000 people who had waited for hours at Chicago's Grant Park, Obama acknowledged the accomplishment and the dreams of his supporters.

"If there is anyone out there who still doubts that America is a place where all things are possible, who still wonders if the dream of our founders is alive in our time, who still questions the power of our democracy, tonight is your answer," he said just before midnight Eastern time.

"The road ahead will be long. Our climb will be steep. We may not get there in one year or even one term, but America, I have never been more hopeful than I am tonight that we will get there. I promise you: We as a people will get there." After the speech he was joined on stage by vice president-elect Sen. Joseph R. Biden Jr. (Del.) and both their families.

The historic Election Day brought millions of new and sometimes tearful voters, long lines at polling places nationwide and celebrations on street corners and in front of the White House. It ushered in a new era of Democratic dominance in Congress, even though the party appeared unlikely to meet its goal of capturing the 60 Senate votes needed for a filibuster-proof majority. In the House, Democrats made major gains, adding to their already sizable advantage and returning them to a position of power that predates the 1994 Republican revolution.

Democrats will use their new legislative muscle to advance an economic and foreign policy agenda that Bush has largely blocked for eight years. Even when the party seized control of Congress two years ago, its razor-thin margin in the Senate had allowed Republicans to hinder its efforts.

McCain congratulated Obama in a phone call shortly after 11 p.m. and then delivered a gracious concession speech before his supporters in Phoenix. "We have had and argued our differences," he said of his rival, "and he has prevailed."

"This is an historic election, and I recognize the special significance it has for African Americans and the special pride that must be theirs tonight," McCain said.

Obama became the first Democrat since Jimmy Carter in 1976 to receive more than 50 percent of the popular vote, and he made good on his pledge to transform the electoral map.

He overpowered McCain in Ohio, Florida, Virginia and Pennsylvania -- four states that the campaign had spent months courting as the keys to victory. He passed the needed 270 electoral votes just after 11 p.m. with victories in California and Washington state.

The Democrat easily won most of the Northeast, the Rust Belt, the West Coast and mid-Atlantic states that normally back Democrats. By midnight, he appeared to be running strong in North Carolina, Indiana, Missouri and Montana, each of which was too close to call. Obama ultimately won in Indiana, bringing his electoral college total to 349, while McCain won Montana, bringing his total to 163 electoral college votes. The outcome in North Carolina and Missouri remained uncertain.